Roll With Rotating Shell

ABSTRACT

The invention relates to a rolling mill roll with a rotating shell consisting of a tubular shell ( 1 ) rotatably mounted on a plurality of pads ( 3 ) holding the shell ( 1 ), whereby a hydrodynamic lift effect is created by introducing a lubricating fluid between the bering face ( 31 ) of the pad ( 3 ) and the internal face ( 13 ) of the shell ( 1 ). 
     According to the invention, the bearing face ( 31 ) of each pad is provided with three hydrostatic pockets, one middle pocket ( 5 ) and two upstream ( 7 ) and downstream ( 6 ) lateral pockets, respectively, which are fed with the same fluid under a pressure sufficient to allow an additional oil flow to be introduced into the dragged out film ( 4 ) with a local pressure increase, in order to broaden—in the upstream and downstream direction—the hydrodynamic lift angular sector ( 4 ) while maintaining, throughout the length thereof, the fluid quantity required for the desired lift effect.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a National Stage entry of International Application No. PCT/FR2004/000954, filed Apr. 16, 2004, the entire specification claims and drawings of which are incorporated herewith by reference.

The invention relates to a roll with rotating shell of the type consisting of a cylindrical tubular shell rotatably mounted about an elongated support beam and bearing on the said beam via holding means, and applies in particular to a back-up roll in a rolling mill for metal strip, especially steel strip.

For some time it has been proposed to use, at first in paper-making and then, more recently, in metal strip rolling mills, rolls with a rotating shell, consisting of a stationary support shaft in the form of an elongated beam, surrounded by a tubular shell rotatably mounted about bearings defining an axis of rotation perpendicular to rolling axis, and bearing on the beam via a plurality of holding means distributed side by side along the length of the beam and centered in an axial bearing plane passing through the roll axis and an external face of the roll, and corresponding to the plane of transmission of the roll force load when the roll is part of a rolling mill.

The tubular shell is relatively deformable and, in the case of a four-high or six-high rolling mill, the use of this type of roll as a back-up roll, by selectively actuating the different holding means, gives the external face of the roll a profile that allows the deflection of the shaft to be compensated and, besides, any fault in the evenness of the surface or in the thickness of the product caused in the course of rolling to be corrected. For this purpose, each means of holding the shell consists of a pad essentially centered in the bearing plane, disposed between the shell and the support beam and slideably mounted on the said support beam in a radial direction essentially extending in the roll load plane. Each pad bears on one side of the internal face of the shell, via a cylindrical bearing face, and on the other side on the support beam via an adjustable thrust means generally consisting of at least one hydraulic cylinder arranged between the support beam and the pad. It is thus possible to regulate the thrust of each pad individually in the radial direction, in order to give the tubular shell the desired profile and/or correct the distribution of thrust forces throughout the external bearing face.

The tubular shell rotates on the bearing faces of the holding pads, and it is therefore necessary to introduce a lubricant between the bearing face of each pad and the internal face of the shell.

For this purpose, each holding pad can be provided, on its bearing face, with at least one hydrostatic pocket consisting of a recess opening towards the outside and fed with a lubricant under a pressure corresponding to the thrust.

As the hydrostatic pocket opens towards the outside, the lubricant fed in the said pocket under pressure may escape toward the edges of the pocket, forming a lubricating film in the gap between the bearing face of the pad and the shell.

This leak rate remains fairly low so long as the external face of the pad is correctly centered with respect to the internal cylindrical face of the rotating shell but the said shell is subjected to stresses likely to cause deformation of the shell in a transverse direction, thereby causing the pad to shift and, consequently, increasing the leak rate. To remedy this, it is proposed in the document GB-A-2 060 822, in addition to the thrust cylinders exerting the main force at pad centre, to incorporate two side cylinders in which pressure may be varied so as to restore the concentricity of the pad with the shell. The pad width, in the transverse direction, is thus slightly increased but the angular sector covered by the circular bearing face does not exceed 45°.

In this case, it is rather difficult to maintain the stability of the pad which, most often, must be linked to the support beam through a hinged-type rod so that it can be kept centered in the axial plane passing through the external bearing face of the shell.

In such known arrangements, the lubricant feeding the hydrostatic pocket is simply taken from the fluid that feeds the thrust cylinder via a channel provided between the cylinder chamber and the hydrostatic pocket.

Such a feeding mode could be appropriate when such devices were used, for example, in the paper industry. However, it was more difficult to apply them to metal strip rolling, in particular steel rolling, as the thrust loads sustained by the roll are extremely high and it is difficult to control the thrust cylinders if there is a variable leak rate for feeding the hydrostatic pocket.

It has thus been proposed, in the document FR-A-2 572 313, to increase the aperture of the angular sector covered by the pad bearing face and to obtain a hydrodynamic effect in the lubricating film arranged in the gap between the said bearing face and the shell, by injecting oil under low pressure at the upstream end of the pad in the direction of rotation of the shell, and with a boosting flow rate which causes the rotating shell to drag out a sufficient quantity of oil so that a continuous oil film is formed in the gap between the shell and the pad, which escapes through the downstream end of the pad. An oil circulation is thus created, which ensures a hydrodynamic lift effect between the pad and the shell, allowing a high pressure to be obtained in the oil film which, in addition, is distributed over a larger surface.

It is thus possible to exert very high thrust forces on the shell, e.g. for steel rolling.

A further advantage of this arrangement is that the lubricant is not fed from the thrust cylinder chamber but through a separate circuit under low pressure. It is thus not necessary, as before, to maintain a leak rate in the high pressure circuit feeding the thrust cylinders.

Besides, as a hydrodynamic lift effect is used, the pressure, which is very low at the upstream end of the gap between the pad and the shell, gradually increases due to the oil drag-out, reaches a peak which is angularly shifted downstream with respect to the roll load plane passing through the external bearing face, then very quickly decreases and becomes nil at the downstream end of the gap, at pad exit. This results in a self-centering of the pad by a wedge effect.

However, prerequisite for obtaining this hydrodynamic lift effect, is that the rotational speed of the shell around the shaft is sufficient to drag along the oil injected upstream. Besides, the injected oil flow must be sufficient to ensure the circulation of the lubricant up to the pad exit by compensating for the lateral leaks.

To avoid the shell contacting the pads in the event of faulty oil feeding or of shell rotation being stopped, it has been proposed in the document FR-A-2 572 313 already mentioned, to arrange a hydrostatic pocket in the central part of the pad, which is fed with a pressurized fluid which, at normal speed, mixes with the oil introduced upstream and carried by the rotating shell, and, at low speed, prevents direct contact by allowing the lubricating film to be formed.

Besides, to adjust the shell profile and the distribution of bearing forces accurately, it is recommended to use a fairly large number of pads. Therefore, the bearing face of each pad which, as described above, must cover a large angular sector, has the form of an elongated rectangle of fairly small width compared with its length.

This results in significant leaks at the side edges of each pad and, consequently, in a pressure drop entailing the risk of breakage of the lubricating film.

The hydrodynamic lift effect created by oil circulation in the gap between the pad and the shell, therefore develops in a pressure area comprising, in the lengthwise direction of fluid circulation, an upstream portion for gradually increasing the fluid pressure from pad entry, a hydrodynamic lift central portion and a downstream portion for quick decrease in pressure at pad exit.

Generally, the central lift part covers an angular sector of the pad subjected to a sufficient pressure to compensate for the global bearing force exerted on the tubular shell by the work roll.

As mentioned above, it is necessary, especially when rolling metallic products, to produce high forces which, in addition, may significantly vary between the individual pads, in order to correct the shape and/or gauge defects found on the rolled strip, downstream of the rolling mill.

Besides, transient excess pressures may occur, especially when threading the strip into the rolling stand or when a weld joining two successive strips, which may have different geometric or metallurgical properties, is passing through.

The use of a hydrodynamic lift effect offers a number of advantages. However, it has been noticed that the various malfunctions that may occur during operation, in particular in the case of rolling, are likely to entail some instability of the pad and also an accidental contact with the shell due to a breakage of the lubricating film. Therefore, it may sometimes be difficult to maintain the reliability of the overall unit at a satisfactory level.

The object of the invention is to remedy such disadvantages by a fairly simple arrangement which allows better control of the hydrodynamic film oil feeding and of pressure distribution on the bearing face of each pad, thus more easily maintaining relatively stable operating conditions.

The invention therefore relates to a roll with a rotating shell of the type consisting of a tubular shell rotatably mounted about a stationary elongated support beam and bearing on the said beam via a plurality of pads, each provided with a cylindrical bearing face having nearly the same radius as the radius of the internal face of the shell, whereby the position and thrust of each pad can be adjusted through a hydraulic cylinder resting, on one side, on the beam, and on the other side, on the pad, and fed with a pressurized fluid, each pad being, in addition, fitted with an hydrostatic pocket provided in a central part of its bearing face and fed with a pressurized fluid, and besides, associated with means of introducing a lubricating fluid upstream of the gap between the pad bearing face and the internal face of the shell, so as to create a hydrodynamic lift effect in a pressure area which covers a large angular sector and comprises, in the shell rotational direction, an upstream portion for gradually increasing the pressure, a lift central portion and a downstream portion for quick decrease in pressure up to pad exit.

According to the invention, the bearing face of each pad is fitted with two lateral pockets opening on both sides of the middle pocket, respectively, and fed with a fluid under a pressure sufficient to allow an additional oil flow to be introduced into the dragged out film with a local pressure increase, in order to broaden—in the upstream and downstream direction—the angular sector covered by the central hydrodynamic lift portion of the pad, thus improving the stability of said pad.

In a particularly advantageous embodiment, each pocket of each pad is associated with a means of calibrating the flow rate input through the relevant pocket, whereby the pressure in said pocket is adjusted to a level at least sufficient to cause the calibrated flow to be discharged at the corresponding level of the fluid film, up to a maximum value of the thrust exerted by the pad on the shell.

Consequently, the central lift part of the pressure area consists of a high pressure central pressure stage covering an angular sector nearly corresponding to the middle pocket, and two lateral pressure stages each extending on an angular sector associated with a lateral pocket, an upstream pressure stage having a lower pressure than that of the central pressure stage and a downstream pressure stage having a pressure between that of the central pressure stage and that of the upstream pressure stage.

In a preferred embodiment, each middle pocket of a pad is individually fed by a pump delivering a calibrated flow and the lateral pockets of all the pads arranged on one side of the middle pocket are supplied in parallel from the same pipe connected to the same pump on which a plurality of individual feed pipes for each pocket, each fitted with a calibrating device for the fluid flow injected through said pocket into the dragged-out film, are connected in parallel.

In a further embodiment, the roll includes at least three units, respectively consisting of the pockets arranged on all pads in the same position with respect to the bearing plane, upstream lateral, central and downstream lateral, respectively, and the pockets of each unit are fed in parallel from a joint piping provided lengthwise on the support beam and on which a plurality of individual feeding pipes for each pocket of said unit respectively, each fitted with an individual flow calibrating device in the corresponding, are connected in parallel.

Besides, a roll with a rotating shell according to the invention can be used, either in a tandem rolling mill in which the product is always running in the same direction, or in a reversing rolling mill operating in both running directions.

If, during operation, the shell rotates in a single rotational direction, the middle pocket of each pad is centered in a radial plane slightly angularly shifted downstream, in the direction of rotation, relative to the bearing plane. In that case, the downstream lateral pocket advantageously covers an angular sector which is nearly twice as large as the sector covered by the upstream lateral pocket.

In the case of a reversing mill, the middle pocket is centered in the bearing plane P and the lateral pockets are symmetrical with respect to said bearing plane. In this case, the calibrated flow rates in both lateral pockets may be equal and the calibrated flow in the middle pocket is advantageously approx. twice as high as the flow rate in each lateral pocket.

Other advantageous features within the scope of protection of the invention will be depicted in the following description of a particular embodiment, given by way of example and shown on the attached drawings.

FIG. 1 is a cross-sectional schematic view of a roll according to the invention applied to a rolling mill.

FIG. 2 is detailed cross-sectional view of a holding pad with associated hydraulic circuits.

FIG. 3 is a bottom view of a holding pad.

FIG. 4 is a longitudinal cross-sectional view of the roll, on which the oil feeding system is schematically shown.

FIG. 5 is a 3-D diagram showing the pressure curve along the bearing face of a pad.

FIG. 1 is a schematic cross-sectional view showing, by way of example, a four-high type rolling mill consisting of two work rolls T, T′ between which the rolled product M passes, and supported on the side opposite to the product on two back-up rolls S, S′ respectively, between which a roll force load is applied along a bearing plane P passing virtually through the roll axes.

At least one of the back-up rolls, e.g. the upper back-up roll S consists of a tubular shell 1 rotatably mounted at its ends, through bearings A, A′ schematically shown in FIG. 4, on a support beam 11 extending inside the tubular shell 1, in a direction transverse to the rolling direction, said bearings A, A′ defining the rotational axis x′x of the shell.

As shown in FIG. 4, the tubular shell 1 bears on the beam 11 through a plurality of holding pads 3 distributed throughout its length and intercalated between the internal cylindrical face 13 of the shell and a lower face 12 of the support beam 11.

Each holding pad 3 is provided, on the tubular shell 1 side, with a cylindrical bearing face 31 of a slightly smaller diameter than the diameter of the inner face 13 of the shell, and bears on the lower face 12 of the beam 11 through at least one hydraulic cylinder 2 which, in the depicted example, includes one piston 22 bearing on the beam 11 and entering into a recess 33 machined on the face 32 of the pad 3 turned toward the beam 11 and constituting the chamber of the hydraulic cylinder 2. Said cylinder is fed with fluid from a hydraulic power station H₁ by a high pressure supply circuit, connected to each pad via a pipe 21 passing through the beam 11 and the piston 22 and opening into the chamber 33 of the associated cylinder.

Each pad 3 is thus associated with a cylinder 2 fed by a special circuit 20, 21, the flow rate and pressure of which can be controlled by a control system on the basis of data transmitted by devices controlling the thickness and profile or flatness of the rolled product M. A detailed description of the equipment and of the hydraulic system does not seem necessary as facilities of this kind have already been built and described in published documents.

Generally, such a system makes it possible, via a position and pressure control of each cylinder 2, to adjust the profile of the external bearing face as well as the distribution of thrust forces applied along said external bearing face, in particular to compensate for the deflection of the support beam 11 and to correct gauge or flatness defects detected downstream on the rolled strip M.

To allow rotation of rotating shell 1 applied on the stationary pads 3, it is necessary to intercalate a lubricating fluid film between the bearing face 31 of each pad 3 and the internal face 13 of the shell.

To this effect, each pad 3 is normally provided with a hydrostatic pocket substantially centered in the bearing plane P and fed with pressurized oil, said pocket widely opening toward the internal face 13 of the tubular shell in order to form a lubricating film 4 between the internal face 13 of the shell 1 and the bearing face 31 of the pad 3.

It should, however, be noted that in the arrangement according to the invention, the bearing face 31 of the pad 3 covers a circular sector with a very wide angular opening larger than 45°, which may exceed 90° and, preferably being in the order of magnitude of 100 or 110°.

Indeed, the distribution of bearing forces over such an aperture angle offers significant advantages.

First of all, as mentioned above, an angular sector having a fairly great length allows a hydrodynamic lift effect to be created in the lubricating fluid film 4. In this case, oil can be fed under low pressure by a booster circuit G, at the upstream end of the pad 3 and, through rotation of the shell 1, is caused to flow into the gap between said shell and the pad 3, with a gradual increase in pressure through wedge effect.

Besides, the fact that the pads 3, distributed across the length of the tubular shell 1, are provided with a large angular opening ensures excellent centering of said shell relative to the beam 11, with a transverse stability effect avoiding transverse deformation of the shell between the end bearings when the product is passing through.

However, to accurately adjust the force distribution along the external bearing face, it is necessary to use a good many adjacent pads, eg seven pads, as shown in FIG. 4. Consequently, to cover a large angular sector, the bearing face 31 of each pad 3 should have a length L1 much greater than its width L2, as shown in FIG. 3.

This results in increasing oil leaks at the side edges of each pad 3, entailing a risk of pressure drop, and breakage of the lubricating film as well.

Indeed, considering the pressure distribution in a direction transverse to the pad, ie parallel to the axis of rotation, it appears that, due to the leakage, said pressure quickly decreases along the side edges of the pad and is at its maximum value only in the central part of the bearing face. Besides, due to a gradual increase of pressure through a hydrodynamic effect, the leak rate increases in the rotational direction and the width of the maximum pressure area therefore decreases between the entry and exit of the bearing face.

In addition, as mentioned above, even in the case of the lift being produced by a hydrodynamic effect with low pressure oil feeding at pad entry, it is advantageous to additionally provide high pressure feeding in the central part of the pad, in the region of bearing plane P, to allow the lubricating film to be formed when the rolling mill is starting up and in case of insufficient rotational speed. To this effect, it is advantageous to provide, in the central part of the pad, a hydrostatic pocket 5 extending over an angular sector, eg 10 to 20°. This central hydrostatic pocket is advantageous, even at high speed, because the fluid fed in the central part of the pad is able to mix with the film dragged out through the hydrodynamic effect if feed pressure exceeds the pressure reached through the hydrodynamic effect in the region of this central pocket 5. It is thus possible to widen the pressure area at this central pocket both in the lengthwise rotational and transverse directions.

From pad entry, the pressure area thus consists of an upstream portion for a gradual increase in pressure, a central part constituting a maximum pressure stage in the region of the central pocket 5 and a downstream portion for quick pressure decrease at pad exit.

Besides, the hydrodynamic lift effect created by the oil film 4 drag-out permits self-centering of the pad because a closure of the gap on the exit side increases the pressure through a wedge effect and, consequently, tends to re-centre the shell with respect to the pad.

However, the leak rate also tends to increase and is likely to cause a breakage of the oil film, thereby causing the pad to contact the shell.

Therefore, this entails a risk of instability which, according to the invention, will be eliminated by introducing an additional pressurized oil flow upstream and downstream of the central pocket 5 in order to widen the angular sector covered by the hydrodynamic lift central part of the pad.

To this effect, as shown in FIGS. 1 and 2, the bearing face 31 of the pad is provided, on each side of the middle pocket 5, with two downstream 6 and upstream 7 lateral pockets respectively and each pocket 5, 6, 7 is associated with a means of calibrating the flow introduced through this pocket under a pressure set to a value at least equal to the hydrodynamic pressure at this level to allow the calibrated flow rate to be discharged into the fluid dragged out by the shell rotation.

Oil injected into the three pockets 5, 6, 7 spaced apart from each other is thus distributed by forming a continuous film nearly throughout the angular sector covered by the bearing face 31, as schematically shown in FIG. 5.

It is thus possible, through adjusting the flow rates in the three pockets 5, 6, 7, to compensate for the leaks occurring, in particular, on the lateral sides of the pads, due to the large angular opening thereof.

To this effect, each pocket 5, 6, 7 is fed at a sufficient pressure to allow the calibrated flow to be discharged and, in the region of each pocket, a local pressure increase occurs, which makes it possible, as explained further, to compensate for the tilting torques sustained by the pad and to ensure stability of said pad in the event of a sudden variation in the applied forces, for example when a weld is passing through the roll gap.

FIG. 1 schematically shows an embodiment of the oil feeding system for each pad 3.

As mentioned above, the thrust cylinders 2 associated with each pad 3 respectively are fed with pressurized fluid from a hydraulic station H₁, by a circuit 20, 21 opening into the chamber 33 of each cylinder 2.

Preferably, the hydrostatic pockets 5, 6, 7 are supplied by pipes 51, 61, 71, respectively, from a second hydraulic power station H₂. It is thus possible to use oils having different viscosity values depending on the application.

As a matter of fact, for ease of operation of the servovalves designed to adjust the thrust forces sustained by the pads 3, it is better that the cylinders 2 should be supplied with a low viscosity oil from the hydraulic station H₁. On the other hand, the hydrostatic pockets 5, 6, 7 can be fed with higher viscosity oil from the second hydraulic station H₂, giving higher hydrostatic lift and less leaks on side edges.

FIG. 1 schematically shows a first embodiment of the circuits 8 a, 8 b for pressurized feeding of the pockets 5, 6, 7.

The lubricant is fed from tank 80 through a pump 83 with fixed delivery, controlled by flow controller 88 and transferred back to the tank through an overfall system including an adjustable permanent leak system 84.

In this embodiment the three pockets 5, 6, 7 of each pad are fed under pressure, each through a pipe 51, 61, 71 respectively, fitted with a flow controller 52, 62, 72 which, during operation, enables oil to be introduced into each pocket with a regulated flow rate at a virtually constant value.

Pressure values in each feed circuit 51, 61, 71 are determined so as to ensure this calibrated oil flow is discharged into each pocket, up to a maximum value of the thrust force likely to be applied on the shell, taking the pocket dimensions into account.

As previously explained, some oil quantity escapes through the lateral edges of the pads but the most part is discharged at the rear end of each pad. The full quantity of oil, however, remains inside the shell 1 which is closed at its ends by the beam 11 and the bearings A, A′. The roll is advantageously provided with a collecting device extending throughout the shell length, above the downstream ends of all pads, in order to collect the oil escaping from the pads and transfer it back, through a return circuit 86, to the hydraulic station H₂.

In FIG. 4, a simple schematic axial sectional view, the pads 3 have been shown with a 90° rotation to represent the feeding circuits for the three pockets which, actually, are centered in the same plane in a direction transverse to the centerline.

Normally, the adjacent pads 3 distributed across the full length of the shell are identical, each consisting of at least three pockets, upstream lateral 7, middle 5 and downstream lateral 6, respectively, and arranged in the same position relative to the bearing plane P.

It is, therefore, particularly advantageous to combine the corresponding pockets into at least three units, downstream lateral E₂, middle E₁ and upstream lateral E₃, the pockets of each unit being fed in parallel from a joint pipe extending along the support beam 11.

As shown in FIG. 2, said joint pipes can be bored in the support beam 11, in a direction parallel to the axis of rotation x′x or the may consist of pipes attached to the side of beam 11.

Moreover, the two pocket units, upstream lateral E₃ and downstream lateral E₂ respectively, can advantageously be supplied under the same pressure from the same pipe 60.

Thus, in the embodiment shown in FIG. 2, the beam 11 is provided with three axial pipes, respectively 20 for feeding the thrust cylinders 2, 50 for feeding the middle pockets 5 and 60 for feeding the upstream 7 and downstream 6 lateral pockets.

Feed circuits 51, 61, 71, associated with each of the pads 3 and which, for reasons of simplification, have been indicated on each side of beam 11 in FIG. 1, advantageously consist of pipes 51 a, 61 a, 71 a bored crosswise in the support beam 11 and connected in parallel to the feed pipe 50 of the unit E₁ of middle pockets 5 and to the feed pipe 60 of the units E₃, E₂ of lateral pockets, upstream 7 and downstream 6.

Transverse pipes 51 a, 61 a, 71 a are connected via flexible hoses 51 b, 61 b, 71 b respectively, each to the associated pipe 51 c, 61 c, 71 c bored in the pad 3 and opening, at one end, on one lateral side of the pad 3 and, at the other end, in the corresponding pocket 5, 6, 7, respectively.

In the embodiment shown in FIGS. 1 and 2, each individual circuit 51 abc, 61 abc, 71 abc is provided with a calibrating device 52, 62, 72 arranged, for example, on the beam 11, at the outlet of the transverse pipe 51 a, 61 a, 71 a, and allowing control of oil injection into the relevant pocket 5, 6, 7, while keeping the exit flow rate constant.

As already explained, the joint pipes 20, 50, 60 are bored longitudinally in the support beam 11 but could also be attached to the beam side.

Chamber 33 of the thrust cylinder of each pad 3 is supplied with high pressure, low viscosity oil from the first hydraulic station H₁ via a circuit 20 which can advantageously pass through a longitudinal bore in the beam 11. Said circuit, including means of individually adjusting the position and pressure of each pad 3, is well known and has, therefore, not been described or shown in details on the drawings.

In this first embodiment, joint pipes 50, 60 are fed, via the hydraulic station H₂, with higher viscosity oil, preferably through two separate circuits, 8 a, 8 b respectively, that enable the unit E₁ of middle pockets 5 on the one hand, and the two lateral pocket units, upstream E₃ and downstream E₂ respectively, on the other hand, to be supplied at different pressures, said pressures being adjusted to ensure continuous oil discharge throughout the bearing surface of pad 3, taking into account the distribution of thrust force and hydrodynamic pressure in the lubricating film 4.

The hydraulic station H₂ also comprises a booster pump 87 for low pressure oil feeding at the entry 34 of the pad 3. The oil introduced through the lateral pockets 6, 7 is, of course, of the same nature and mixes with the lubricating film 4 dragged out due to the shell rotation.

Each pump 83 a, 83 b is associated with a flow controller 88 a, 88 b, with an overfall device 84 a, 84 b. In this way, if the hydrodynamic pressure in the film 4 is sufficient at each point to ensure the hydrodynamic lift, the oil supplied by pumps 83 a, 83 b is returned to the tank. On the other hand, if the flow in the film 4 turns to be insufficient, due to leaks, to ensure the lift, for instance in the event of a speed decrease or of a sudden increase in the force applied, the calibrated flow rate is delivered by the corresponding pocket and mixes with the dragged out fluid in order to compensate for the leaks and to increase the pressure.

Generally, the rolling mill is designed to operate within a given rolling force range and the feed pressures in joint pipes 50, 60 as well as the calibrated flow rates introduced into each pocket 5, 6, 7 through the individual circuits 51, 61, 71 are determined so as to ensure that oil is discharged and a continuous film is formed throughout the adjusting range of the thrust force exerted on each pad by the cylinder 2, up to a maximum value which depends on the working conditions and on such parameters as—in case of strip rolling—the width and thickness of said strip, material temperature and properties, as well as the reduction in thickness to be obtained.

The hydraulic feeding mode shown in FIG. 1 is fairly economical as the hydraulic station H₂ feeding the pockets 5, 6, 7 uses only two medium pressure pumps, 83 a for the middle pockets and 83 b for the lateral pockets, respectively.

However, to guarantee the stability of pads, eg in case of sudden variation in the rolling force, it may be preferable, in a further improved embodiment, to use, for each pad, one pump for individual feeding of the middle pocket that sustains the bulk of the thrust force, in order to calibrate the oil flow to the required pressure at each pad.

FIG. 4 schematically shows such an embodiment consisting of a pumping unit 9 which comprises as many pumps 91 as there are pads 3, each pump 91 feeding the middle pocket of a pad at the pressure required for discharging the calibrated flow, taking into account the thrust force applied on the shell 1 in the region of the relevant pad.

As depicted above, the two lateral pocket units E₂, E₃ can be fed through the same pump 83 by a circuit 8 similar to the one that has previously been described with reference to FIG. 1.

Advantageously, this circuit 8 may include, downstream of the pump 83, a safety block 84 which limits the common pressure to the required level and a device 88 for measuring and controlling the global flow rate in the two units E₂, E₃ of lateral pockets of the pads 3.

FIG. 5 is a 3D-diagram showing, for a half pad placed on one side of the middle plane Q perpendicular to the axis of rotation, the pressure curve on the ordinate axis, as a function of the angular position along the bearing face 31 of the pad, indicated after development of said bearing face along the horizontal abscissa axis.

In the embodiment shown in FIG. 5, the upstream lateral pocket 7 covers an angular sector of approx. 10°, having its middle plane P1 inclined at approx. 25° relative to the bearing plane P on which the middle pocket 5 is centered, and the middle plane P2 of the downstream pocket 6, which also covers a sector of approx. 10°, is inclined at approx. 20° relative to said vertical bearing plane P.

The middle pocket 5 is centered on the bearing plane P and covers an angular sector of approx. 20°.

The pad, however, remains of the type shown in FIG. 2 and, therefore, comprises means of introducing, at the entry 34 of the pad, a lubricating fluid which is dragged out by the rotation of shell 1 and creates a hydrodynamic lift effect.

Generally, the pressure diagram includes, as usual, an upstream zone A for gradual increase of the fluid pressure, a central zone B of maximum pressure and a downstream zone C for fast pressure decrease at exit of the pad. However, the two lateral pockets 7, 6 significantly modify the shape of parts A and C of the diagram by creating therein two pressure stages, upstream 41 and downstream 42, respectively, on each side of a central pressure stage 40 corresponding to the middle pocket 5.

As the oil introduced at low pressure at the entry 34 of the pad is gradually carried along, its hydrodynamic pressure is not very high at the upstream pocket 7 and may be, for example, in the embodiment shown, of the order of magnitude of 1/7 of the maximum pressure in the middle pocket 5. However, the fact that an additional fluid quantity is injected at this level, which mixes with the lubricating film dragged along by the rotation, increases the pressure of said film and allows the upstream part A of the hydrodynamic lift zone to be widened in the upstream direction.

Besides, as mentioned above, the fact that the width L₂ of the pad is small compared to its length L₁ causes lateral oil leaks and the maximum pressure area tends to tighten in the direction of rotation of the shell. Introducing an additional oil flow through the upstream pocket 7 is a means of compensating for this leakage and, consequently, of longitudinally and transversely widening the central pressure stage 40, which can thus cover a length and a width fairly close to the dimensions of the middle pocket 5.

After exiting said middle pocket 5, the leak rate further increases and the oil escapes from the gap between pad and shell with a risk of contact with the exit of the pad.

However, as shown on the diagram, the oil introduced through the downstream pocket 6 must be at a fairly high pressure, higher than the pressure of the upstream pocket 7, and this additional calibrated oil flow permits the part C of the hydrodynamic lift zone to be widened in the downstream direction, thus avoiding any risk of contact with the pad and the shell. In practice, pressure in the downstream pocket 6 may be about half the maximum pressure in the middle pocket 5.

The angular sector covered by the hydrodynamic lift zone is thus widened in the upstream and downstream directions. Besides, injecting a pressurized fluid into the two lateral pockets 6, 7 causes, by hydrostatic effect, thrust forces F₁, F₂ centered on the middle radial planes P₁, P₂ of both pockets 6, 7 which are inclined at a minimum angle of 20° relative to the bearing plane P.

Expansion of the hydrodynamic lift angular sector and the fact that the shell is supported on three distant points considerably improves the stability of each pad. The back-up roll is thus able to sustain sudden variations in the thrust force applied by the work roll, without any risk of shift of the shell 1 and of contact between said shell and the external faces 13 of pads 3.

Of course, the invention is not limited to the details of the embodiments that have just been described by way of a simple example and alternative embodiments could be included without deviating from the scope of protection of the invention.

In particular, it is possible to vary the angular sectors covered by the different pockets, and their angles of inclination relative to the middle plane. To reach the desired stability effect, the hydrodynamic lift zone should, however, cover a large angular sector, approx. one quadrant and, anyway, of at least 45° to 50°.

Besides, should the shell always rotate in the same direction, it would be better that the middle plane P₁ of the downstream pocket 6 be more inclined with respect to the bearing plane P than the middle plane P₂ of the upstream pocket 7. In addition, the middle pocket 5 could be slightly shifted in the downstream direction, in the direction of rotation of the shell 1, in order to compensate for the deformation of the associated work roll in the reverse direction while the product is passing through. In this case, the middle plane P of the middle pocket 5 would be slightly inclined with respect to the vertical plane.

However, this invention may also advantageously apply to the construction of reversing mills in which the rolls and, consequently the tubular shell 1, are rotating alternately in one direction and the other.

In that case, the arrangement would be symmetric, as the middle pocket 5 is centered on the vertical plane passing through the axis and the two lateral pockets 6 and 7 are equal and centered on inclined planes of the same angle relative to the vertical line, on each side thereof.

The reference marks inserted after the technical data mentioned in the claims are only aimed to facilitate the understanding thereof and do not constitute a limitation of the scope thereof. 

1. Roll with a rotating shell consisting of: a stationary support (11) in the form of an elongated beam, a tubular shell (1) having an internal face (13) and a cylindrical external face, surrounding the support beam (11) and rotatably mounted on said beam around a rotation axis, said shell being subjected to thrust forces distributed along an external face and directed virtually along a bearing plane (P), a plurality of pads (3) holding the shell (1), intercalated between the internal face (13) of said shell and a bearing face of the support beam (11) and distributed, side by side, across the shell length, each pad (3) being shiftable along a radial direction passing through the rotation axis and comprising a cylindrical bearing face (31) having a radius nearly equal to that of the internal face (13) of the tubular shell (1) and extending over a large aperture angular sector, means of individually adjusting the position and thrust of the pads (3) comprising, for each pad (3), at least one hydraulic cylinder (2) intercalated between the beam and the pad (3) and connected to a first pressurized fluid feeding circuit (20), at least one hydrostatic pocket (5) provided in a middle part of the bearing face (31) of the pad and connected to a second pressurized fluid feeding circuit (50), means of introducing, in a gap between the bearing face (31) of the pad (3) and the internal face (13) of the shell (1), a lubricating fluid forming a continuous film dragged out by the rotation of the shell (1) whereby a hydrodynamic lift effect is created in a pressure area (4) extending over a large aperture angular sector and comprising, in the direction of rotation of the shell (1), an upstream part (A) for gradually increasing the fluid pressure from pad entry, a maximum pressure central part B covering an angular sector substantially corresponding to the middle pocket (5), and a downstream part (C) for quick decrease in pressure up to pad exit, characterized in that the bearing face (31) of each pad is provided with two lateral pockets, upstream (7) and downstream (6), opening on each side of the middle pocket (5) and supplied with fluid under a pressure sufficient to allow an additional oil flow to be introduced into the dragged out film with a local pressure increase, in order to broaden—in the upstream (4) and downstream direction—the hydrodynamic lift angular sector (4) by maintaining, throughout the length thereof, the fluid flow rate required for the desired lift effect.
 2. Roll with a rotating shell as claimed in claim 1, characterized in that each pocket (5, 6, 7) of each pad (3) is associated with a means of calibrating the flow introduced through the relevant pocket, the pressure in said pocket being adjusted at a value at least sufficient to cause the calibrated flow to be discharged at the corresponding level of the fluid film (4), up to a maximum value of the thrust exerted by the pad (3) on the shell (1).
 3. Roll with a rotating shell as claimed in claim 2, characterized in that the fluid introduced under pressure through the two lateral pockets (6, 7) determines thrust forces centered on two radial planes (P₁, P₂) inclined on each side of the bearing plane (P) and likely to maintain the pad stability.
 4. Roll with a rotating shell as claimed in claim 1, characterized in that the hydrodynamic lift zone (4) of the pad includes a high pressure central pressure stage extending over an angular sector substantially corresponding to the middle pocket (5), and two lateral pressure stages corresponding to the two lateral pockets (7, 6) respectively, one upstream pressure stage (41) in the upstream pressure increase part (A) and one downstream pressure stage (42) in the downstream part (C) for pressure decrease in the lift zone (4).
 5. Roll with a rotating shell as claimed in claim 4, characterized in that the upstream lateral pocket (7) is fed at a pressure lower than the pressure in the middle pocket (5) and that the downstream lateral pocket (6) is fed at a pressure between middle pocket (5) and upstream pocket (7) pressures.
 6. Roll with a rotating shell as claimed in claim 4, characterized in that the fluid introduced at the level of the upstream pressure stage (41) causes the hydrodynamic pressure to increase more rapidly as a result of the increased quantity of dragged out fluid and determines a longitudinal and transverse widening of the high pressure central pressure stage (40) by leak rate compensation in this region.
 7. Roll with a rotating shell as claimed in claim 6, characterized in that the fluid introduced in the region of the downstream pressure stage (42) causes the hydrodynamic lift zone (4) to widen as a result of the increased quantity of fluid dragged out up to pad (3) exit.
 8. Roll with a rotating shell as claimed in claim 2, characterized in that each middle pocket (5) is fed individually by a pump delivering a calibrated flow rate.
 9. Roll with a rotating shell as claimed in claim 8, characterized in that the lateral pockets (6) (7) of all pads (3) arranged on the same side of the middle pocket (5) are supplied in parallel from a common pipe connected to one single pump on which a plurality of individual fed pipes for each pocket are connected in parallel, each fitted with a device (62) (72) for calibrating the fluid flow injected through said pocket into the dragged out film.
 10. Roll with a rotating shell as claimed in claim 2, characterized in that it comprises at least three units (E₃, E₁, E₂) consisting of the pockets arranged on all the pads (3) in the same position relative to the bearing plane (P), lateral upstream (7), middle (5) and lateral downstream (6), respectively, and the pockets of each unit (E₃, E₁, E₂) are fed in parallel from a joint pipe (71, 51, 61) provided along the support beam (2) and on which a plurality of individual pipes feeding each pocket of the unit (E₃, E₁, E₂), are connected in parallel, each fitted with an individual device (72, 52, 62) for calibrating the flow rate in the corresponding pocket (7, 5, 6).
 11. Roll with a rotating shell as claimed in claim 10, characterized in that the two lateral pocket units (E₃, E₂), upstream (7) and downstream (6) respectively, are fed in parallel from a common pipe (60) and that the fluid feed circuit consists of two branches, a first branch feeding all middle pockets (5) via a first common pipe (50) and a second branch feeding all lateral pockets (6, 7) via a second common pipe (60).
 12. Roll with a rotating shell as claimed in claim 11, characterized in that each pocket unit (75, 55, 65) is associated with an open-circuit controlled feeding system, comprising one pumping device (83) for feeding the circuit with a global flow rate under a common pressure, said flow rate and said pressure being adjusted to levels at least sufficient to cause the calibrated flow rates to be discharged through all the pockets of the unit up to a maximum value of the thrust force exerted by the shell (1).
 13. Roll with a rotating shell as claimed in claim 2, characterized in that the calibrated flow rates introduced through the two lateral pockets (6, 7) of each pad (3) are nearly equal and that the calibrated flow introduced through the middle pocket (5) is nearly twice as high as the flow in each lateral pocket (6, 7).
 14. Roll with a rotating shell as claimed in claim 1, in which the tubular shell (1) rotates, during operation, in a single direction relative to support beam (2), characterized in that the middle pocket (5) of each pad (3) is centered in a radial plane slightly angularly shifted downstream, in the direction of rotation, with respect to the bearing plane (P).
 15. Roll with a rotating shell as claimed in claim 14, characterized in that the downstream lateral pocket (6) covers an angular sector of the bearing face (31) nearly twice as large as the sector covered by the upstream lateral pocket (7).
 16. Roll with a rotating shell as claimed in claim 15, characterized in that the lateral pocket (7) arranged upstream, in the direction of rotation of the shell (1) covers a sector of approx. 10° centered in a radial plane inclined at about 20° relative to the bearing plane (P) and that the lateral pocket (6) arranged downstream covers a sector of approx. 20° centered in a plane inclined at about 30° relative to the bearing plane (P).
 17. Roll with a rotating shell as claimed in claim 1, characterized in that the bearing face of each pad (3) covers an angular sector of about one quadrant, up to 100°-110°.
 18. Roll with a rotating shell as claimed in claim 1, characterized in that it is operated hydrostatically from stop to a maximum shell rotation speed, the fluid flow injected through each of the three pockets (5, 6, 7) of each pad (3) being adjusted so as to maintain a continuous oil film throughout the surface of the pad, considering that said oil is dragged out by the rotating shell (1).
 19. Roll with a rotating shell as claimed in claim 1, characterized in that it constitutes at least one of the back-up rolls in a rolling stand for metallic strip. 